A new twist on feeling the blues

One of the most fascinating aspects of nature is how organisms evolved defense mechanisms over time. Like felines’ retractable claws or the Komodo dragon’s septic mouth, some mechanisms adopt the view that a good offense makes the best defense. Others are more reactionary, such as a lizards’ ability to detach appendages at the first sign of trouble or other creatures’ ability to blend in with their surroundings by changing color. Many of our ectothermic friends, including cephalopods, amphibians, and reptiles, are able to camouflage themselves at will to mitigate risk. But how many of these colorful creatures use this ability to help them see?

A group of researchers from the University of North Carolina Wilmington, Florida International University, and Duke University have made an interesting discovery concerning the hogfish, or Lachnolaimus maximus, which is endemic to the western Atlantic Ocean from North Carolina to Brazil.

Courtesy of iStock.com/mtilghma.

Using a photosensitive protein called opsin, hogfish skin can change to the color and pattern of its habitat. It does this by absorbing short-wavelength light through its skin, which the protein translates to chromatophores in the skin layers above. This determines what pigment to apply to prevent the hogfish from ending up on somebody’s menu.

To be clear, hogfish scales can’t technically “see,” like the proverbial second-grade teacher that claims to have eyes in the back of their head. That said, there is a biological twist to the hogfish’s camouflaging abilities. Unlike other animals who use dynamic color changing, the skeletal structure of a hogfish inhibits it from looking at itself. Instead, researchers suggest a hogfish’s opsin could be acting as an imageless Polaroid to help with this vertebrate-centric setback.

As the researchers scrutinized the fish’s skin, they found that the opsins didn’t reside within the chromatophore cells but within separate previously undiscovered cells. They estimated that the opsin molecules in hogfish skin are most sensitive to blue light. This is significant because the blue wavelengths are absorbed the best by the pigments in the chromatophores. These pigments, along with red, yellow, or black, bunch up or spread out depending on what color they are trying to match, filtering where light can penetrate the skin to get to the opsins.

Essentially, the researchers believe that this mechanism creates sensory feedback that lets the hogfish sense its own skin as it changes color, allowing it to fine-tune its tone to match the surroundings it sees with its eyes.

The hope is that this discovery might lead to feedback techniques for devices such as robotic limbs or self-driving cars. Or maybe, just maybe, it could also be used to help out those second-grade teachers.

The research was published in Nature Communications (www.doi.org/10.1038/s41467-023-40166-4).